NATURAL HISTORY 





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These photographs were taken from the same spot on the Mohave desert floor. 

 The upper was made at the end of the rainy season, the lower about two months 

 later. What one factor causes this difference.!^ 



noticed a recently formed epiphragm over the mouth of one of these snails. 

 On removing the snails from the tablet and placing them in tepid water, one 

 of them came out of its shell, and the next day ate some cabbage leaf. A 

 month or two afterwards it began repairing the lip of its shell, which was 

 broken when it was first affixed to the tablet." 



